Voltage-gated potassium channels constitute the major ionic conductance detected in both excitable and non-excitable cells and are important players in cellular processes like regulation of ion balance, membrane potential, secretion and cell excitability (Lan et al., Cancer Biol. Ther. 2005, 4, 1342). Such events can mediate or trigger certain signaling cascades, resulting in cellular processes of great diversity.
Certain cells of the immune system, for example, require a complex interplay of different ion channels in order to convert a pathogenic stimulus into an appropriate action like proliferation and/or cytokine secretion. Especially in T- and B-lymphocytes, this type of activation triggers a calcium signal within the cell, which has to be maintained for an extended period in order to result in transcriptional activity and thus a completion of the activation program. For T-cells, the activation via the T-cell receptor (TCR) triggers a signaling cascade resulting in the calcium release from the endoplasmatic reticulum into the cytosol. This release triggers the opening of the CRAC (Ca2+-release activated channel), enabling a strong calcium influx into the cell. For maintaining such a calcium influx for an extended period of time, which is required for an efficient T-cell response on a cellular level, potassium has to be released from the cytosol.
For this purpose, T-cells are equipped with two potassium channels, the KCa3.1(IK-1), which is calcium-gated and thus opens upon increasing cytosolic calcium concentrations, and Kv1.3, which is voltage-gated and opens due to the depolarization of the membrane potential caused by the calcium influx. Both act together for potassium efflux, now allowing for further calcium influx via CRAC into the cell. This interplay of CRAC, IK-1 and Kv1.3 is crucial for an activation of lymphocytes to result in proliferation and/or cytokine production (Lewis, Annu. Rev. Immunol. 2001, 19, 497; Vig et al., Nat. Immunol. 2009, 10, 21; Feske et al., Nat. Rev. Immunol. 2012, 12, 532).
Different T- and B-cell subsets display different expression numbers of IK-1 and Kv1.3, of which class-switched memory B-cells and repeatedly activated effector memory T-cells (TEM cells; CD4+T-cells and CD8+T-cells) are dominated by Kv1.3. These lymphocyte subsets are of the Kv1.3highIK-1low phenotype, in which Kv1.3 expression numbers of 1000 to 2900 channels per cell were found, whereas IK-1 channel numbers in these cells are clearly below 100. In contrast, other activated T- and B-cell subsets display rather similar expression numbers for Kv1.3 and IK-1 of several hundred per cell each, and in some instances even with a favour of IK-1 (for further information see the review articles listed below).
Inhibition of Kv1.3 is thus effective in decreasing lymphocyte proliferation and/or cytokine production in lymphocytes of the Kv1.3highIK-1low phenotype, whereas other lymphocyte subsets are expected not to respond significantly (for further information see the review articles listed in the following paragraph and Shah et al., Cell. Immunol. 2003, 22, 100).
Several review articles deal with Kv1.3 channel architecture, distribution in human tissues and cell types and the pharmacological potential in its inhibition to treat diseases, including: Wulff et al., Chem. Rev. 2008, 108, 1744; Lam et al., Drug Dev. Res. 2011, 72, 573; Wang et al., Pharmacother. 2013, 33, 515.
TEM cells of the Kv1.3highIK-1low phenotype have been postulated to be the crucial subset of disease-mediating lymphocytes in T-cell driven autoimmune disorders (for further information see the review articles listed in the preceding paragraph). This has been directly demonstrated within isolates from human patients with, e.g., Type 1 diabetes (T1D; PNAS 2006, 103, 17414), rheumatoid arthritis (RA; PNAS 2006, 103, 17414), multiple sclerosis (MS; J. Clin. Invest. 2003, 111, 1703; PNAS 2005, 102, 11094), psoriasis and psoriatic arthritis (J. Invest. Dermatol. 2011, 131, 118; J. Autoimmunity 2014, 55, 63), and anti-glomerular basement membrane glomerulonephritis (Am. J. Physiol. Renal Physiol. 2010, 299, F1258). In PBMCs isolated from patients with acute coronary syndrome (ACS), the number of CD4+CD28null T-cells was significantly higher than in healthy controls and directly correlated with hs-CRP levels in these patients. This disease relevant T-cell subset significantly overexpressed Kv1.3 in these patients (Huang et al., J. Geriatric Cardiol. 2010, 7, 40) and was identified to consist mainly of TEM cells (Xu et al., Clin. Immunol. 2012, 142, 209). Within induced sputum form asthma patients, increased levels of TEM cells were identified, being of the Kv1.3high phenotype (Koshy et al., J. Biol. Chem. 2014, 289, 12623).
TEM cells have also been reported to be important contributors to disease development and/or progression in chronic diseases like anti-neutrophil cytoplasmic autoantibody (ANCA) associated vasculitis (AAV; Abdulahad et al., Arthritis Res. Ther. 2011, 13, 236; Wilde et al., Arthritis Res. Ther. 2010, 12, 204), systemic lupus erythematosus (SLE; Dolff et al., Ann. Rheum. Dis. 2010, 69, 2034), Graft-versus-Host disease (Yamashita et al., Blood 2004, 103, 3986; Zhang et al., J. Immunol. 2005, 174, 3051; Beeton et al., Neuroscientist 2005, 11, 550), Inflammatory Bowel Diseases (IBDs; Kanai et al., Am. J. Physiol. Gastrointest. Liver Physiol. 2006, 290, G1051) including Crohn's disease (de Tena et al., J. Clin. Immunol. 2004, 24, 185; Beeton et al., Neuroscientist 2005, 11, 550), autoimmune thyroiditis and Hashimoto disease (Seddon et al., J. Exp. Med. 1999, 189, 279; Beeton et al., Neuroscientist 2005, 11, 550), Uveitis including pars planitis (Pedroza-Seres et al., Br. J. Ophthalmol. 2007, 91, 1393; Oh et al., J. Immunol. 2011, 187, 3338; Beeton et al., Neuroscientist 2005, 11, 550), alopecia areata (Gilhar et al., J. Invest. Dermatol. 2013, 133, 2088), vitiligo, pemphigus foliaceus, inclusion body myositis, dermatomyositis, and scleroderma (Beeton et al., Neuroscientist 2005, 11, 550). Furthermore, the important role of class-switched memory B-cells for disease pathogenesis has also been described for T1D, RA and MS (Wulff et al., J. Immunol. 2004, 173, 776), Grave and Hashimoto disease, and Sjögren syndrome (Beeton et al., Neuroscientist 2005, 11, 550). In addition, Kv1.3 inhibitors have been reported to inhibit CD8+TEM/TEMRA cell differentiation and proliferation and their Granzyme B release, and linked to a reduction of their neurotoxicity and thus to a potential treatment of neuroinflammatory disorders like MS (Wang et al., PLoS One 2012, 7, e43950; Hu et al., PLoS One 2013, 8, e54267).
Furthermore, Kv1.3 has been identified in other cell types of the immune system like macrophages (DeCoursey et al., J. Membrane Biol. 1996, 152, 141; Villalonga et al., Biochem. Biophys. Res. Commun. 2007, 352, 913), microglia (Eder, Am. J. Physiol. Cell Physiol. 1998, 275, C327; Menteyne et al., PLoS One 2009, 4, e6770; Pannasch et al., Mol. Cell. Neurosci. 2006, 33, 401), dendritic cells (Zsiros et al., J. Immunol. 2009, 183, 4483), non-adherent natural killer cells (Koshy et al., PLoS One 2013, 8, e76740), in cells of the CNS like human neural progenitor cells (Wang et al., J. Neurosci. 2010, 30, 5020; Peng et al., J. Neurosci. 2010, 30, 10609), postganglionic sympathetic neurons (Doczi et al., Am. J. Physiol. Regul. Integr. Comp. Physiol. 2008, 295, 733), select central and peripheral neurons, neurons in the nucleus of the solitary tract (Ramirez-Navarro et al., J. Neurophysiol. 2011, 105, 2772), and oligodendrocytes (Tegla et al., Exp. Mol. Pathol. 2011, 91, 335.). With regard to microglia, their neurotoxic effect upon activation with either HIV-1 glycoprotein gp120 or HIV-1 Tat protein was abrogated upon treatment with Kv1.3 inhibitors, which underlines their potential for therapy of HIV-1-associated neurocognitive disorders (HAND) and other inflammation-mediated neurological disorders (Liu et al., Cell Death Dis. 2012, 3, e254; and PLoS One 2013, 8, e64904). Furthermore, priming of microglia by amyloid-β resulting in reactive oxygen species (ROS) production upon secondary stimulation was inhibited by treatment with Kv1.3 inhibitors, thus rendering Kv1.3 channels potential targets to reduce microglia-induced oxidative stress in Alzheimer's disease (Schilling et al., J. Cell. Physiol. 2011, 226, 3295). Furthermore, Kv1.3 inhibition was shown to decrease microglia migration (Nutile-McMenemy et al., J. Neurochem. 2007, 103, 2035). Concerning macrophages, Kv1.3 inhibitors were shown to e.g. modulate cholesterol-metabolism-associated molecules thus inhibiting macrophages' differentiation into foam cells, which represents a strategy for the treatment of atherosclerosis (also known as arteriosclerotic vascular disease or ASVD) (Yang et al., J. Lipid Res. 2013, 54, 34).
Kv1.3 has also been identified in retinal ganglion cells (Koeberle et al., Cell Death Diff. 2010, 17, 134), platelets and megakaryocytes (McCloskey et al., J. Physiol. 2010, 588, 1399; Emerson, J. Physiol. 2010, 588, 1809), and tumorigenic human mammary epithelial cells (Jang et al., BMB reports 2009, 42, 535), human ovarian cancer cells like SKOV3 (Weng et al., Prog. Mod. Biomed. 2011, 11, 2053), human lung adenocarcinoma cells A549 (Jang et al., Eur. J. Pharmacol. 2011, 651, 26), brown adipose tissue and hepatocytes (Upadhyay et al., PNAS 2013, 110, E2239) and skeletal muscle cell lines (Hamilton et al., J. Physiol. Sci. 2014, 64, 13). In addition, Kv1.3 was reported to represent a potential sensor of metabolism within the olfactory bulb (Fadool et al., PLoS One 2011, 6, e24921; Tucker et al., J. Physiol. 2013, 10, 2541 and J. Neuroendocrinol. 2012, 24, 1087). Furthermore, Kv1.3 was identified in the inner membrane of mitochondria, where they are involved in the intrinsic apoptosis pathway, and their inhibition was evaluated for the treatment of chronic lymphocytic leukemia (B-CLL) (Leanza et al., Leukemia 2013, 27, 1782), osteosarcoma, neuroblastoma and melanoma (Leanza et al., EMBO Mol. Med. 2012, 4, 577; Wu et al., Int. J. Mol. Sci. 2013, 14, 19245; Leanza et al., Curr. Pharmaceut. Design 2014, 20, 189), and suggested for the depletion of tumor-associated macrophages (Leanza et al., Curr. Med. Chem. 2012, 19, 5394). Inhibitors of Kv1.3 were also shown to potently suppress migration and proliferation of vascular smooth muscle cells, which might represent a new principle for the treatment of restenosis/neointimal hyperplasia (Jackson, Arterioscler. Thromb. Vasc. Biol. 2010, 30, 1073; Cheong et al., Cardiovasc. Res. 2011, 89, 282; Olschewski, Cardiovasc. Res. 2011, 89, 255; Cidad et al., Arterioscler. Thromb. Vasc. Biol. 2012, 32, 1299; Ishii et al., Free Rad. Biol. Med. 2013, 65, 102; Cidad et al., Pflugers Arch. Eur. J. Physiol.; DOI 10.1007/s00424-014-1607-y).
Kv1.3 expression has also been shown to be a potential disease marker in biopsies of inflamed mucosa from ulcerative colitis patients and correlated with certain cytokine expression levels (Hansen et al., J. Crohn's Col. 2014, 8, 1378).
A Kv1.3 inhibitor has been shown to decrease activation levels of Th2-cells and cytotoxic CD8+T-cells in PBMCs from patients with acute ischemic stroke (AIS), potentially reducing its unwanted clinical consequences (Folyovich et al., CNS Neurol. Disorders Drug Targets 2014, 13, 801).
For CD4+T lymphocytes from PBMCs isolated from patients with essential hypertension, a chronic low-grade inflammatory disease, increased Kv1.3 expression levels compared to undiseased control group were reported (Li, Exp. Clin. Cardiol. 2014, 20, 5870).
Efficacy of Kv1.3 inhibitors has been reported in relevant animal models for autoimmune diseases like Psoriasis, MS, alopecia areata, rheumatoid arthritis, type I diabetes, allergic and irritant contact dermatitis (Azam et al., J. Invest. Dermatol. 2007, 127, 1419; Ueyama et al., Clin. Experiment. Dermatol. 2013, 38, 897; Kundu-Raychaudhuri et al., J. Autoimmunity 2014, 55, 63), anti-glomerular basement membrane glomerulonephritis (as a cause of rapidly progressive glomerulonephritis), and also for asthma, chronic kidney disease, renal fibrosis in chronic renal failure and end-stage renal disease (Kazama, J. Physiol. Sci. 2015, 65, 25; Kazama et al., Int. J. Nephrol. 2012, article ID 581581), and for melanoma, obesity, insulin resistance, and neuroprotection and neurorestoration (Peng et al., Neuro-Oncology 2014, 16, 528). A Kv1.3 inhibitor was reported to reduce tumor volume in a xenograft model using the human lung adenocarcinoma cells A549 (Jang et al., Eur. J. Pharmacol. 2011, 651, 26), and to decrease intimal hyperplasia formation, indicating a therapeutic potential against restenosis (Cidad et al., Cardiovasc. Drugs Ther. 2014, 28, 501). Kv1.3 inhibition prevented plaque formation and decreased exocytosis of cytoplasmic granules from CD4+CD28null T-cells in a rat model for atherosclerosis, revealing a potential for suppression of the development of atherosclerosis and prevention of acute coronary syndrome (Wu et al., Heart Vessels 2015, 30, 108).
A combination of an IK-1 inhibitor and a Kv1.3 inhibitor has been shown to be effective in preventing transplant rejection in an animal model (Grgic et al., Transplant. Proc. 2009, 41, 2601). A similar effect was reported for the Kv1.3 inhibitor Correolide C within a vascularized composite allotransplantation (VCA) model (Hautz et al., Transplant. Int. 2013, 26, 552). Kv1.3 inhibition has also been shown to be effective in preventing T-cell mediated inflammatory bone resorption disease (Valverde et al., J. Bone Miner. Res. 2004, 19, 155).
Certain small molecule Kv1.3 inhibitors have been reported. For a brief overview, cf. Wulff et al., Chem. Rev. 2008, 108, 1744; and Wulff et al., Nat. Rev. Drug Disc. 2009, 8, 982. Furthermore, certain compounds were published as Kv1.3 inhibitors, belonging to scaffolds like sulfonamides (WO2011/073269, WO2011/073273, WO2011/073277, WO2010/130638, WO2010/023448), spiro compounds (WO2010/066840), pyrazoles and imidazoles (WO2007/020286), dioxidobenzothiazols (Haffner et al., Bioorg. Med. Chem. Lett. 2010, 20, 6983 and 6989; WO2005/11304), and phenanthridines (Pegoraro et al., Bioorg. Med. Chem. Lett. 2009, 19, 2299 and 2011, 21, 5647).
Out of this set of compounds, especially certain khellinones (Baell et al., J. Med. Chem. 2004, 47, 2326; Harvey et al., J. Med. Chem. 2006, 49, 1433; Cianci et al., Bioorg. Med. Chem. Lett. 2008, 18, 2055; WO03/078416; WO2006/096911; WO2008/040057; WO2008/040058; WO2009/043117; WO2009/149508) and the psoralen derivative PAP-1 (Vennekamp et al., Mol. Pharmacol. 2004, 65, 1364; Schmitz et al., Mol. Pharmacol. 2005, 68, 1254; Bodendiek et al., Eur. J. Med. Chem. 2009, 44, 1838; WO2006/041800; U.S. Pat. No. 7,772,408) have been evaluated with regard to their potential as Kv1.3 inhibitors.
Furthermore, certain Kv1.3 inhibitors have been described in the field of cardiovascular pathologies, particularly in the field of diseases derived from hyperplasia of the tunica intima (WO2010/040803) and for application in neurodegenerative diseases, in particular for neuroprotection and stimulation of neural growth (WO2007/139771) and reduction of microglia-mediated neurotoxicity (WO2012/170917). Kv1.3 inhibitors have also been reported to affect weight control, control of body fat and food intake and thus for treating obesity, diabetes and insulin insensitivity (WO2002/100248). Furthermore, a combination treatment of a Kv1.3 inhibitor with a pre-implantation factor peptide for the treatment of intracellular damage resulting from e.g. Lyme disease, cardiovascular disease, duodenal peptic ulcer, atherosclerosis or tuberculosis was described (WO2012/119072). WO2013/052507 describes targeting the Kv1.3 channel as a treatment for obesity and obesity-related disorders.
Syntheses of certain 5-phenyl-furo[3,2-g]coumarin (that is 4-phenyl-psoralen) derivatives have been described in the literature, usually involving a Pechmann cyclization and a McLeod's reaction. Cf. for example Ansary, Bull. Fac. Pharm. Cairo Univ. 1998, 36, 85; Garazd et al., Chem. Nat. Comp. 2000, 36, 478; Garazd et al., Chem. Nat. Comp. 2002, 38, 539; Traven et al., Heterocyclic Commun. 1997, 3, 339; Pardanani et al., J. Ind. Chem. Soc. 1969, 46, 1014. A specific route for inverting the anellation order of the lacton-ring and the furan is described in Kawase et al., Bull. Chem. Soc. Jpn. 1978, 51, 1907-1908; Zhang et al., Eur. J. Med. Chem. 2010, 45, 5258. A synthetic route towards certain furo[3,2-g]quinolin-7(8H)-one, thieno[3,2-g]coumarin, 6H-chromeno [6,7-d]oxazol-6-one (i.e. oxazolocoumarin) and 8-azapsoralen derivatives is described in Guiotto et al., Il Farmaco 1995, 50, 479; Chilin et al., Gazz. Chim. Ital. 1988, 118, 513, and Rodighiero et al., J. Heterocyclic Chem. 1998, 35, 847, however, these compounds were all equipped only with methyl substituents.
Certain specific psoralens, and xanthotoxin in particular, have been described for their potential photobiological activities and for their use in photochemotherapy (PUVA=psoralen+UVA irraditation) (Pathak et al., J. Invest. Dermatol. 1959, 32, 255; Juettermann et al., Farmaco, Edizione Scientifica 1985, 40, 3; Toth et al., J. Photochem. Photobiol. B Biol. 1988, 2, 209; Nofal et al., Pakistan J. Scientific Ind. Res. 1990, 33, 148; Tuveson et al., Photochem. Photobiol. 1992, 56, 341; Becker et al., J. Chem. Soc. Faraday Trans. 1993, 89, 1007; Körner, Arch. Pharm. Med. Chem. 2002, 5, 187). Such investigations have also been performed for certain 5-phenyl-furo[3,2-g]coumarin (that is 4-phenyl-psoralen) derivatives: Farag, Eur. J. Med. Chem. 2009, 44, 18; Lown et al., Bioorg. Chem. 1978, 7, 85; Ansary, Bull. Fac. Pharm. Cairo Univ. 1998, 36, 85. For specific linear furo[3,2-g]quinolone, thieno[3,2-g]coumarin, 8-azapsoralen and thieno-[3,2-g]-8-aza-coumarin derivatives, such a photobiological effect has also been investigated: Guiotto et al., J. Heterocyclic Chem. 1989, 26, 917; Guiotto et al., Il Farmaco 1995, 50, 479; Aubin et al., J. Invest. Dermatol. 1991, 97, 50 and 995; Vedaldi et al., Il Farmaco 1991, 46, 1407.
Furthermore, certain 5-phenyl-furo[3,2-g]coumarins are reported to have potential in treating or preventing diseases caused or mediated by helicobacter pylori (CN102091067, Zhang et al., Eur. J. Med. Chem. 2010, 45, 5258), in treating diabetes mellitus and complicating diseases thereof (CN101307056), for controlling coccids (JP63057590), and as inhibitors of NFkB and its functions in cystic fibrosis (Piccagli et al., Bioorg. Med. Chem. 2010, 18, 8341).
With regard to furoquinolones, certain biological activities have only been reported for 4-methylbenzofuro[3,2-g]quinolin-2(1H)-one: As inhibitor of FKBP52-enhanced steroid receptor activity (WO2011/034834), as inhibitor of ABCG2 protein for a method of enhancing treatment of tumor cells with a chemotherapeutic agent (WO2009/061770), and to stimulate or inhibit the binding to and lipid movements mediated by SR-BI and redirect uptake and metabolism of lipids and cholesterol by cells (WO2004/032716).
With regard to the treatment of inflammatory diseases driven by repeatedly activated TEM cells, especially autoimmune diseases, general immunosuppressants are utilized in currently applied treatment regimens (e.g. mycophenolate mofetil, cyclophosphamide, cyclosporine A, azathioprine, etc.) resulting in a general suppression of lymphocytes, thus increasing the risk for opportunistic infections. Furthermore, longterm treatment often results in side effects reducing the overall compliance (e.g. skin atrophy and enhanced risk of osteoporosis with glucocorticoid treatment, increased risk of skin cancer and rhabdomyolysis upon topical tacrolimus treatment, nausea and vomiting with cyclophosphamide and cyclosporine A). Recent approvals of medicaments for the treatment of such diseases include several biologics (e.g. Alefacept, Natalizumab, Adalimumab, Ustekinumab, Belimumab), which display a potential for a general side effect profile known for such drugs like sensitization, anaphylactic shock, resistance, and again often showed an enhanced risk for opportunistic infections.
There is, therefore, a need for new small molecule medicaments which, compared with the aforementioned therapeutics, are particularly more selective towards specific cell subsets of the immune system and particularly avoid the aforementioned adverse effects, in particular in the therapy of the above medical conditions.